The use of CO2 which can be recovered in value as carbon source for the production of chemical consumables is a key challenge in order to decrease its accumulation in the atmosphere but also in order to control our dependence on fossil fuels.
The greatest challenge faced by scientists and manufacturers is that of recycling CO2, that is to say of developing reactions which make it possible to produce chemical compounds, such as, for example, fuels, plastic polymers, medicaments, detergents or high-tonnage molecules traditionally obtained by petrochemical methods. The technical difficulty lies in the development of chemical reactions which make it possible to functionalize CO2 while reducing the central carbon (i.e., while replacing the C—O bonds of the CO2 with C—H or C—C bonds).
The catalytic reduction of CO2 to give formic acid HCOOH, formaldehyde H2CO, methanol CH3OH and methane CH4 is arousing increasing interest in the search for novel synthetic fuels. In this context, the main reduction processes can be classified according to the nature of the reducing agent used, as shown in sections 1 to 4 below. The use of powerful reducing agents, such as alkali metals (Li, Na, K) or metal hydrides (aluminum hydride, borohydrides, and the like), is ruled out as these reactants result in highly exothermic reactions in the presence of CO2 and thus do not make it possible to provide a favorable energy balance in the reduction of carbon dioxide.
1. Electrochemical and Photoelectrochemical Methods
The use of electrons provided by an electrolysis assembly in order to reduce CO2 remains a highly dynamic field of research which is motivated by the hope of finding efficient and selective catalysts which make it possible, for example, to selectively reduce CO2 in the presence of protons while avoiding the formation of molecular hydrogen H2 (E. E. Benson, C. P. Kubiak, A. J. Sathrum and J. M. Smieja, Chem. Soc. Rev., 2009, 38, 89). Photoelectroreduction processes are also being studied (Y. Izumi, Coord. Chem. Rev., 2013, 257, 171).
2. Hydrogenation of CO2 
The reaction between CO2 and molecular hydrogen can result in the formation of formic acid (in the presence of a base), of methanol or of methane. Molecular catalysts (homogeneous catalysts) and heterogeneous catalysts have been described for facilitating this reaction (P. G. Jessop, T. Ikariya and R. Noyori, Chem. Rev., 1995, 95, 259; W. Wang, S. Wang and J. Gong, 2011, 3703).
3. Hydrosilylation of CO2 
The reaction between CO2 and hydrosilanes (characterized by the presence of an Si—H bond) makes it possible to reduce CO2 to give formoxysilane, bis(silyl)acetals and methoxysilanes which can result, after hydrolysis, in formic acid HCOOH, in formaldehyde H2CO and in methanol CH3OH respectively (S. N. Riduan, Y. G. Zhang and J. Y. Ying, Angew. Chem. Int. Ed., 2009, 48, 3322; A. Berkefeld, W. E. Piers and M. Parvez, J. Am. Chem. Soc., 2010, 132, 10660). Some catalysts also make it possible to directly reduce CO2 to methane (T. Matsuo and H. Kawaguchi, J. Am. Chem. Soc., 2006, 128). In these reactions, siloxanes and silanols are formed as by-products.
4. Hydroboration of CO2 
The reaction between CO2 and a hydroborane of formula (I) is referred to as hydroboration reaction of CO2. This conversion requires the use of a catalyst. Three different catalytic systems are known to date. They are described in detail below.                The group of Hairong Guan (University of Cincinnati, USA) developed the first catalyst for the hydroboration of CO2 in 2010 (S. Chakraborty, J. Zhang, J. A. Krause and H. R. Guan, J. Am. Chem. Soc., 2010, 132, 8872; S. Chakraborty, Y. J. Patel, J. A. Krause and H. R. Guan, Polyhedron, 2012, 32, 30; S. Chakraborty, J. Zhang, Y. J. Patel, J. A. Krause and H. R. Guan, Inorg. Chem., 2013, 52, 37). It is a nickel complex which makes it possible to carry out the reduction of CO2 to give methoxyborane. Formoxyborane is observed as reaction intermediate. The hydroboranes used are catecholborane (catBH), 9-borabicyclo[3.3.1]nonane (9-BBN) and pinacolborane (pinBH). The catalyst operates at ambient temperature in the presence of 1 bar of CO2. With catecholborane, the Turn-Over Number (TON, defined below) of the catalyst is 495 at 25° C. and its Turn-Over Frequency (TOF, defined below) is 495 h−1. This reaction is shown in scheme 1 below.        

In the scheme above and in the continuation of the account, TON and TOF are defined as follows:
      TON    =                            amount          ⁢                                          ⁢          of          ⁢                                          ⁢          borane          ⁢                                          ⁢                      (                                          R                1                            ⁢                              R                2                            ⁢              BH                        )                    ⁢                                          ⁢          at          ⁢                                          ⁢          the          ⁢                                          ⁢          end          ⁢                                          ⁢          of          ⁢                                          ⁢          the          ⁢                                          ⁢          reaction                          amount          ⁢                                          ⁢          of          ⁢                                          ⁢          borane          ⁢                                          ⁢                      (                                          R                1                            ⁢                              R                2                            ⁢              BH                        )                    ⁢                                          ⁢          at          ⁢                                          ⁢          the          ⁢                                          ⁢          start          ⁢                                          ⁢          of          ⁢                                          ⁢          the          ⁢                                          ⁢          reaction                    ×              100                  catalytic          ⁢                                          ⁢          charge          ⁢                                          ⁢          in          ⁢                                          ⁢          mol          ⁢                                          ⁢          %                          TOF    =                            amount          ⁢                                          ⁢          of          ⁢                                          ⁢          borane          ⁢                                          ⁢          at          ⁢                                          ⁢          the          ⁢                                          ⁢          end          ⁢                                          ⁢          of          ⁢                                          ⁢          the          ⁢                                          ⁢          reaction                          amount          ⁢                                          ⁢          of          ⁢                                          ⁢          borane          ⁢                                          ⁢          at          ⁢                                          ⁢          the          ⁢                                          ⁢          start          ⁢                                          ⁢          of          ⁢                                          ⁢          the          ⁢                                          ⁢          reaction                    ×              100                  catalytic          ⁢                                          ⁢          charge          ⁢                                          ⁢          in          ⁢                                          ⁢          mol          ⁢                                          ⁢          %                    ×              1                  reaction          ⁢                                          ⁢          time          ⁢                                          ⁢          in          ⁢                                          ⁢          hours                    
Thus, the higher TON and TOF, the more effective the catalyst.                In 2012, the group of Sylviane Sabo-Etienne (CNRS, Toulouse, France) described a catalyst based on a ruthenium hydride complex for the hydroboration reaction of CO2 (S. Bontemps, L. Vendier and S. Sabo-Etienne, Angew, Chem. Int. Ed., 2012, 51, 1671). The authors showed that the hydroboration reaction of CO2 could result in intermediates of bis(boryl) acetal and boroxymethyl formate (R1R2B—OCH2OCHO) types. These intermediates were not isolated.        Only pinacolborane was used and a high catalyst charge was used (10 mol %). Under these conditions, the activity of the catalyst is low and the formation of methoxyborane requires 22 days of reaction at ambient temperature or 5 h at 70° C. This reaction is shown in scheme 2 below.        
                In 2012, the group of Douglas W. Stephan (University of Toronto, Canada) described a ruthenium-based catalyst for the hydroboration of CO2 (M. J. Sgro and D. W. Stephan, Angew. Chem. Int. Ed., 2012, 51, 11343). Catecholborane and 9-borabicyclo[3.3.1]nonane were used as reactants. They did not show a difference in reactivity. The reaction is slow at 50° C. with a catalyst load of 1.0 mol %. This reaction is shown in scheme 3 below.        
                Conversions involving reaction promoters (such as Mes3P/AlCl3 or Mes3P/AlBr3 (Mes=mesityl) mixtures) in stoichiometric amounts, that is to say, non-catalytic amounts, have also been described by G. Ménard and D. W. Stephan, J. Am. Chem. Soc., 2010, 132, 1796.        
The conversion of CO2 to chemical consumables, such as, for example, methane derivatives, in particular oxygen-comprising, halogen-comprising or amine-comprising methane derivatives, especially formic acid, formaldehyde and methanol, methane, methyl halide and methyl amine, by a hydroboration reaction of CO2 is arousing increasing interest. The reaction of CO2 with a hydroborane, which takes place in two stages, results in advantageous synthetic intermediates of formoxyborane (R1R2BO—CHO), methoxyborane (R1R2B—O—CH3) or bis(boryl) acetal ((R1R2B—O)2CH2) type. These intermediates, which can also be more generally denoted as “oxyborane compounds” as a result of the presence of “R1R2B—O—” in these compounds, are stable and readily lend themselves to various types of reactions in order to result in varied chemical compounds, such as formic acid, formaldehyde, methanol, methane, methyl halide, methyl amine, and the like.
However, due to the high thermodynamic stability of carbon dioxide, its conversion into oxyborane compounds necessarily has to involve effective catalysts so as to promote the thermodynamic balance of this chemical conversion.
Furthermore, the hydroboration reaction requires the use of an effective catalyst as, in its absence, the product resulting from this chemical conversion cannot be obtained in a measurable fashion in a short period of time (less than one week) and at a temperature of less than 150° C.
In point of fact, to date, hydroboration reactions of CO2 deploy a limited number of catalysts which, moreover, are essentially complexes of transition metals which are often expensive and/or toxic, such as nickel or ruthenium.
In the context of the conversion of CO2 by a hydroboration reaction, first into “oxyborane compounds” and then into chemical consumables, such as, for example, methane derivatives, in particular oxygen-comprising, halogen-comprising or amine-comprising methane derivatives, especially formic acid, formaldehyde, methanol, methane, methyl halide and methyl amine, the technical challenge to be taken up is that of developing effective catalysts which overcome the problems of toxicity and of costs generally associated with the use of known metal catalysts, in particular catalysts based on precious metals.
There thus exists a real need for a catalyst which makes possible the conversion of CO2 and a hydroborane into oxyborane compounds, by a hydroboration reaction, which is effective (capable of increasing the rate of the conversion of the CO2 even in a low amount), selective (promoting the production of the desired product in comparison with the by-products) and not very expensive and/or not very toxic compared with the catalysts known for the conversion of CO2 into oxyborane compounds by this type of reaction.
In particular, there exists a real need for a catalyst, as defined above, which does not comprise:                alkaline earth metals from Group IIA of the Periodic Table of the Elements (such as magnesium and calcium);        transition metals from Group IB to VIIIB of the Periodic Table of the Elements (such as nickel, iron, cobalt, zinc, copper, rhodium, ruthenium, platinum, palladium or iridium);        rare earth metals, the atomic number of which is between 57 and 71 (such as lanthanum, cerium, praseodymium or neodymium); or        actinides, the atomic number of which is between 89 and 103 (such as thorium or uranium).        
Furthermore, oxyborane compounds incorporating radioisotopes and/or stable isotopes and capable of being converted into different labelled chemical compounds, such as formic acid, formaldehyde, methanol, methane, methyl halide, methyl amine, and the like, are of particular interest in many fields, such as, for example, in life sciences (study/elucidation of enzymatic mechanisms or of biosynthetic mechanisms, in biochemistry, and the like), environmental sciences (tracing of wastes, and the like), research (study/elucidation of reaction mechanisms) or the research and development of novel pharmaceutical and therapeutic products. Thus, to develop a process for the preparation of labelled oxyborane compounds meeting the requirements indicated above can meet a real need.
There thus exists a real need to have available a process which makes it possible to prepare labelled oxyborane compounds incorporating radioisotopes and/or stable isotopes starting from labelled reactants, such as, for example, labelled CO2 and/or a labelled hydroborane.